In Lovecraft's day, the physical sciences were causing a substantial reimagining of the quality and quantity of the universe. For the 10,000 years previous, man had employed a pretty basic rule to understand his world: what you see is what you get. The material world was made up of obvious, mostly solid components, and little thought had to be applied to understand their properties. 20th century science challenged that presumption on two fronts. For one, science began to understand that the universe was much smaller than previously understood (in the sense that physical material broke down into molecules, atoms, photons and other units which could not be seen with the naked eye) and much bigger (in the sense that the universe seemed endless.) Secondly, science was offering ever more proof that our senses, particularly our eyes, offered only a bare glimmer of reality. There were clearly many elements such as the full spectrum of light, x-rays and radiation which we could not observe unless aided with additional technologies.

These observations fit in well with Lovecraft's particular brand of fiction, a sub genre of suspense which he named "cosmic horror." Cosmic horror is, as described by this Wikipedia article on Lovecraft, "the idea that life is incomprehensible to human minds and that the universe is fundamentally inimical to the interests of mankind."

The idea that there was more to the world than meets the eye had been around since before the 20th century, of course. In the early 1600s Galileo had used telescopes to observe the surface of the celestial bodies in our solar system. Not much later, Anthony Leeuwenhoek of Holland developed a microscope that could see bacteria and blood cells. But telescopes and microscopes only augmented objects whose existence we had some sense of. In 1895, the physicist Wilhelm Rontegen discovered x-rays --- energy waves that are similar to light waves, but, because they are much shorter than light waves, are invisible to human vision. Rontegen thoroughly investigated x-rays and realized that they could be used to "photograph" the interior of the human body (a discovery with numerous applications in the world of medicine.)

However, x-rays also had a downside; in 1927, the scientist Hermann Muller discovered that x-rays could lead to genetic mutations. By bombarding male fruit flies with radiation, he was able to induce an unnatural amount of mutation in their progeny. Muller presumed that as the radiation passed through the chromosomes of cells, it disrupted the long strands of molecular DNA containing what we call genes. (Genes are, in essence, biological codes responsible an organism's traits and abilities such as eye color or the ability to speak well*.)

This concept --- that an invisible, unknowable force could change the function and behavior of biological life --- sounds as if it's right out of an H.P. Lovecraft story. In fact, it is a Lovecraft story, one of his most famous, "The Colour Out of Space." In this tale, a mysterious "radiation" significantly alters the function and appearance of both plant and human life. (In "The Colour..." the force isn't quite invisible, but it does defy human senses and, as Lovecraft explains, is best imagined as an analogue of color.) Beyond Lovecraft, Muller's discovery had great influence in the world of comic books. Spider-Man, the Fantastic Four and the Hulk were all characters whom once had been normal but gained superpowers due to exposure to one form of radiation or another. (The same could be said of a famous giant lizard named Godzilla.) Like Lovecraft, comic authors realized that radiation played into a understandable human fear: the fear of the invisible. Radiation posed the possibility that even when things seemed fine they were going horribly wrong. (Always a safe assumption in my book.)

During the same era as Muller's radioactive x-rays, the scientific theory of quantum physics was shaking foundations. Quantum physics upended several aspects of man's then understanding of the universe, not least of all Isaac Newton's classical every-action-has-a-cause physics. I'm the first to admit I understand only parts of quantum physics; one aspect of it posits that electromagnetic forces such as light behave (in some ways) the way that particles of matter behave. For our purposes here, it should be understood that quantum physics deals with the universe on a microscopic level, far removed from the ability of the human senses to directly perceive it. And, as if to further unseat our trust in our senses, in 1927, quantum physicist Werner Heisenberg offered up his "uncertainty principle" which essentially placed limits on how much an observer could possibly know about a moving particle. This theme, that there are limits to knowledge, was also a theme in the fiction of Lovecraft. Recall, again, the description of cosmic horror... "the idea that life is incomprehensible to human minds."

Moving from the very small to the very big, we must note that the 20th century was a fruitful period for the sciences of the stars: astronomy and cosmology. Lovecraft was an avid follower of astronomy and wrote many nonfiction essays with titles like "Trans-Neptunian Planets" or "My Opinion As to the Lunar Canals." (He wrote of the discovery of Pluto as "a thing which excites me more than any other happening of recent times. Its existence is no surprise, for observers have long known that one or more such worlds probably exist beyond Neptune; yet its actual finding carries hardly less glamour on that account.")

As man expanded his understanding of the size of the universe, the obvious question arose: were there other forms of life out there? The most famous fantasy author to explore this query was H.G. Wells with his "The War of the Worlds," but Lovecraft also made alien lifeforms a prominent part of his fiction. Lovecraft dealt not so much with individual aliens, but entire races such as the Great Race from "The Shadow Out Of Time" or the Old Ones from "At the Mountains of Madness." Without fail, Lovecraft's aliens were so superior to humans that we warranted --- at best --- only a passing glance from them, usually while they carried forth some scheme that would result in our total destruction.

If a constantly expanding universe billions of galaxies wide wasn't big enough, 20th century cosmologists and philosophers also theorized the concept of "the multiverse." The multiverse embrace the possibilities of many overlapping universes that could intersect at key points. In Lovecraft's short story "From Beyond" (later expanded into a film directed by Stuart Gordon) a character opens a portal between a parallel universe which allows denizens from a foreign dimension to enter our reality. In "The Shunned House" a character comments that "scientific study and reflection had taught us that the known universe of three dimensions embraces the merest fraction of the whole cosmos of substance and energy." Clearly the ideas of the multiverse were not lost on Lovecraft.

It's the sciences of astronomy and cosmology that probably had the biggest effect on Lovecraft's writing. Integral to these disciplines is the notion that Earth, and man, are but tiny components in the grand scheme of all known reality. This theme deeply resonated with Lovecraft; human tragedies, suffering, victories and defeats --- the subjects of most fiction --- were not of interest to him. He once stated...

... all my tales are based on the fundamental premise that common human laws and interests and emotions have no validity or significance in the vast cosmos-at-large. To me there is nothing but puerility in a tale in which the human form - and the local human passions and conditions and standards - are depicted as native to other worlds or other universes. To achieve the essence of real externality, whether of time or space or dimension, one must forget that such things as organic life, good and evil, love and hate, and all such local attributes of a negligible and temporary race called mankind, have any existence at all.